This invention relates to gas filled puffer switches and more particularly to rotary puffer switches that are easier to manufacture in a low cost manner and without sacrifice of performance characteristics.
The prior art includes the following U.S. Pat. Nos. 2,757,261; 3,214,550; 3,749,869; 3,947,650; 4,268,890; 4,484,047; 4,490,594; 4,523,253; 4,527,029; 4,659,886; European Patents: 0,171,352; 0,214,083; West German Patents: 1,290,223; 2,333,895; PCT application No. 89/11746; and Siemens 8DJ10 Ring Main Units.
In general, a puffer switch is a gas filled (usually high voltage) device which contains contacts that might be subject to arcing or corona discharge when they open or close. Such arcing can cause the contacts to erode and perhaps to disintegrate over time. In some atmospheres, the arc might cause an explosion. Therefore, a known practice is to fill the device with an inert, electrically insulating gas which quenches the arcing. As the switch moves its contacts in an arc-causing motion, the gas is compressed. A jet or nozzle is positioned so that at the proper moment during contact movement, a draft or blast of the compressed gas is directed toward the location of the arc in order to extinguish it.
Once an arc has formed, it is extremely difficult to extinguish until the arc current is substantially reduced. In alternating current (AC) systems, the line current is reduced to zero twice during each AC cycle. As the current approaches zero, the stream of insulating gas cools and deionizes the gas in the arc zone, and may mechanically disrupt the ionized path. Once the arc has been initially extinguished, the cooling and deionizing effect of the gas stream rapidly increases the dielectric strength of the gas in the arc zone, thereby preventing re-ignition of the arc.
Sulphur hexafluoride (SF6) is a gas which is often used in such gas filled switches. Sulphur hexafluoride (SF6) is a chemically and physiologically inert, non-flammable gas which has arc-quenching capability. If a draft of SF6 is blown through the area where an arc occurs, even at low velocities, the arc-quenching effectiveness is greatly multiplied as compared to the effectiveness of the same gas in a still air condition. Also, the interrupting ability of the gas is improved by increasing the pressure of the gas in the switch chamber and therefore, the velocity of the draft of gas.
Most of the prior art puffer switches were simple devices having a plunger which moved longitudinally into or out of contact with a set of stationary contacts. This type of structure was inherently limited as to size and as to the number, combination, or sequence of contacts that could be opened or closed without great sophistication or expense. A rotary puffer switch is more flexible since a large number, combination, and sequence of openings and closings may be built into the switch. However, the prior art rotary puffer switches were more complicated, expensive to build, and difficult to assemble. One problem with these known gas filled rotary switches has been that they required highly complex molded and machined piece parts. Also, the mechanism for compressing the gas and for directing a puff or draft of the gas onto the arc area has not always produced the draft as efficiently as it could have produced it.